As hepatitis C virus (HCV) therapeutic antiviral regimens continue to improve and as the benefits of viral eradication become more apparent, the need to increase treatment success rates becomes ever more important. Standard-of-care (SOC) treatment regimens that include pegylated interferon (peg-IFN) and ribavirin are lengthy, have significant side effects, and do not benefit all patients. Recently completed phase 2 trials have demonstrated improved efficacy of new agents, such as HCV protease inhibitors and polymerase inhibitors. Phase 3 trials are underway and there may soon be FDA approval of new combination therapies, including the protease inhibitors telaprevir or boceprevir combined with peg-IFN and ribavirin. Despite these recent advances, there remains an underlying need to understand the fundamental mechanisms of the human immune response to HCV infection, both to maximize the benefits of currently available treatments and to contribute to the knowledge base necessary to develop more effective therapies. The mission of the Clinical Epidemiology Core is to support and facilitate the Center's two integrated research Projects on innate and adaptive immunity. The Core will (a) identify, enroll, and obtain a blood sample from a diverse group of 200 patients with retrospectively defined outcomes of peg-IFN/ribavirin treatment in the years 2005-2009 for HCV genotype 1 (GT-1); (b) enroll and obtain consecutive blood samples from a diverse prospective cohort of 80 treatment-naive patients initiating combination antiviral therapy for HCV GT-1 in the years 2011-2014; and (c) provide hepatology and clinical research expertise to the Center's overall goals, including the development of patient-related protocols and the administration of all aspects of human subjects protection. In addition, the Core will develop and maintain the Center's biorepository and comprehensive study databases and provide epidemiological, biostatistical, and data analysis expertise to (a) develop analytic databases for the Center's projects and (b) conduct the intra- and inter-project analyses of the immunological correlates of antiviral treatment responses.